David L. Thorn

Bio: David L. Thorn is an academic researcher from DuPont. The author has contributed to research in topics: Rhodium & Triisopropylphosphine. The author has an hindex of 17, co-authored 28 publications receiving 1647 citations. Previous affiliations of David L. Thorn include Osaka University & Cornell University.

Ethylene complexes. Bonding, rotational barriers, and conformational preferences

Abstract: Rotational barriers and conformational preferences are a primary probe of bonding in olefin complexes. Such bar- riers in ethylene-ML2-s are analyzed in terms of differential interactions between the frontier orbitals of the ML, fragment and the ethylene 7r and x*. It is found that the large barrier to internal rotation about the M-ethylene axis in ethylene-ML2 complexes, favoring the in-plane orientation, is due to loss of overlap between ethylene 7r* and an ML2 b2 orbital-the domi- nant interaction in these compounds. An analogous situation exists for rigid rotation in ethylene-ML4 within the trigonal-bipy- ramidal geometry. A much lower energy pathway for this complex is found if rotation is accompanied by pseudorotation. The barrier in square-planar ethylene-ML3 compounds of the Zeise's salt type, on the other hand, is largely set by steric factors which favor the upright geometry. Various strategies are devised to lower the barrier or reverse the conformational preference in these complexes. This may be accomplished by changing the electronic or steric properties of the ligands on the metal or the ethylene. Finally unsymmetrically substituted olefin complexes are examined. In the ML3 case the metal-carbon bond to the carbon bearing the weaker donor or weaker acceptor should be the stronger or shorter one. In the ML2 and ML4 complexes of ethylene the acceptor effect is accentuated, that of the donor less important.

The olefin insertion reaction

Abstract: A molecular orbital study of the insertion of ethylene into a Pt-H bond begins with an analysis of the interaction of a hydride with an ethylene in the absence of the metal. Identification of the crucial orbitals along a simplified reaction coordinate allows one to focus on how the metal atom with one to three other ligands attached to it facilitates the insertion. Associative and dissociative processes from a four-coordinate reactant lead to five- and three-coordinate intermediates whose complex po- lytopal rearrangements are explored in detail. We do not find an easy insertion pathway from a five-coordinate intermediate, nor a facile reaction by a direct route from a four-coordinate complex with ethylene and hydride trans to each other. The neces- sary final waypoint of ethylene and hydride cis seems in the calculations to be best achieved by a sequence of associative and, preferably, dissociative steps.

Cyclization of diacetylenes to E,E exocyclic dienes. Complementary procedures based on titanium and zirconium reagents

Abstract: La cyclisation intramoleculaire de composes diyniques a ete effectuee en utilisant l'une des combinaisons de reactifs: Cp 2 TiCl 2 /PMePh 2 /Na(Hg) ou Cp 2 ZrCl 2 /Mg/HgCl 2

The heck reaction as a sharpening stone of palladium catalysis.

Abstract: s, or keywords if they used Heck-type chemistry in their syntheses, because it became one of basic tools of organic preparations, a natural way to

Utilisation of CO2 as a chemical feedstock: opportunities and challenges

Abstract: The need to reduce the accumulation of CO2 into the atmosphere requires new technologies able to reduce the CO2 emission. The utilization of CO2 as a building block may represent an interesting approach to synthetic methodologies less intensive in carbon and energy. In this paper the general properties of carbon dioxide and its interaction with metal centres is first considered. The potential of carbon dioxide as a raw material in the synthesis of chemicals such as carboxylates, carbonates, carbamates is then discussed. The utilization of CO2 as source of carbon for the synthesis of fuels or other C1 molecules such as formic acid and methanol is also described and the conditions for its implementation are outlined. A comparison of chemical and biotechnological conversion routes of CO2 is made and the barriers to their exploitation are highlighted.